1. Field of the Invention
The present invention relates generally to optical waveguide fibers having improved resistance to bending, and particularly to waveguide fibers having large effective area, and negative total dispersion in the 1550 nm operating window, and improved resistance to macro-bend and micro-bend
2. Technical Background
A waveguide having large effective area reduces non-linear optical effects, including self phase modulation, four wave mixing, cross phase modulation, and non-linear scattering processes, which can cause degradation of signals in high power systems. In general, a mathematical description of these non-linear effects includes the ratio, P/A.sub.eff, where P is light power. For example, a non-linear optical effect can follow an equation containing a term, exp [PxL.sub.eff /A.sub.eff ], where L.sub.eff is effective length. Thus, an increase in A.sub.eff produces a decrease in the non-linear contribution to the degradation of a light signal propagating in the waveguide.
The requirement in the telecommunication industry for greater information capacity over long distances, without regenerators, has led to a reevaluation of single mode fiber refractive index profile design.
The focus of this reevaluation has been to provide optical waveguides that reduce non-linear effects such as those noted above and are optimized for the lower attenuation operating wavelength range around 1550 nm, i.e., the range from about 1250 nm to 1700 nm. In addition the waveguide should be compatible with optical amplifiers, and, retain the desirable properties of optical waveguides now deployed, such as, high strength, fatigue resistance, and bend resistance.
A waveguide fiber having at least two distinct refractive index segments has been found to have sufficient flexibility to meet or exceed the criteria for a high performance waveguide fiber system. The genera of segmented core designs are disclosed in detail in U.S. Pat. No. 4,715,679, Bhagavatula.
The effective area of a waveguide is in general increased by designing refractive index profiles that cause the light power distribution in the fiber to be shifted outwardly from the centerline of the waveguide fiber, thus reducing the power density. In moving the power distribution outwardly toward the core edge, however, the waveguide is made more susceptible to power losses due to bending of the fiber.
Bending losses have been found to occur in the cabling process as well as in the installation process. In some waveguide fiber uses, at least a part of the waveguide is installed as a coil, for example, in a junction box.
Thus there is a need for an optical waveguide fiber that reduces the non-linear term of refractive index by increasing effective area, A.sub.eff, while maintaining a desired resistance to macrobend and microbend.